Tuesday, February 5, 2013

Hello Protocol

The hello protocol  is a fundamental protocol for wired and wireless networks. In mobile ad-hoc networks, a hello protocol helps nodes to establish a neighbor table for link detection. If nodes exchange position information in hello packets, then it also helps them in packet forwarding decisions. In ad-hoc networks, due to node mobility, neighbor relationships change frequently. To cope with mobility, and to have an up-to-date neighbor table, nodes advertise hello packets periodically. These hello packets create congestion, which may cause control and data packets to be dropped in the network.

The Hello Protocol works differently on broadcast networks, as compared to non-broadcast networks. On broadcast networks, each router advertises itself by periodically multicasting Hello Packets. This allows neighbors to be discovered dynamically. These Hello Packets contain the router's view of the Designated Router's identity, and the list of routers whose Hello Packets have been seen recently. On non-broadcast networks some configuration information is necessary for the operation of the Hello Protocol. Each router that may potentially become Designated Router has a list of all other routers attached to the network. A router, having Designated Router potential, sends Hello Packets to all other potential Designated Routers when its interface to the non- broadcast network first becomes operational. This is an attempt to find the Designated Router for the network. If the router itself is elected Designated Router, it begins sending Hello Packets to all other routers attached to the network.

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